1. Field of the Invention
This invention relates to winches having a powered rotatable drum for winding in and releasing a cable or the like and more particularly to a winch system of the type in which the drum is driven and controlled by means of fluid pressure-operated clutches and brakes.
2. Prior Art
Prior application Ser. No. 334,354 of L. F. Yates et al., filed Feb. 21, 1973 for "WINCH WITH FREE-WHEELING DRUM" now abandoned and co-pending application Ser. No. 662,320 of L. F. Yates et al., filed Mar. 1, 1976 for "WINCH WITH FREE-WHEELING DRUM" as a continuation-in-part of application Ser. No. 334,354, both assigned to the assignee of the preent application, disclose a winch assembly which is driven by an engine through a drive train having a normally disengaged input clutch which engages in response to fluid pressure to enter a Reel-In mode where it reels in cable. The driven train also includes a normally engaged brake for immobilizing the winch drum and providing a Brake-On mode but which releases in response to fluid pressure in other modes of operation. In addition to the Brake-On and Reel-In modes of operation, the brake alone may be pressurized to effect a Brake-Off mode in which load forces pulling on the line may unwind cable against the limited resistance created by the drag of the drive train components. This limited resistance prevents excess unwinding of cable caused by a load, by drum momentum, or motivated by other causes, but is sufficiently strong that it is difficult or impossible to withdraw cable manually while such resistance is present. Accordingly, the drive train connects to the winch itself through a disconnect clutch which is normally engaged but which may be disengaged by fluid pressure to allow manual unreeling of cable from the drum without working against a substantial resistance thus providing a Free-Spool (or Disconnect) mode. This form of winch assembly is highly useful on a log skidder vehicle, for example, which is used to drag logs from the site of a lumbering operation and also has substantial advantages in other contexts.
Prior U.S. Pat. No. 3,841,608 discloses a hydraulic control system for a winch assembly of this kind in which a manually operated control valve may be shifted between a series of positions to pressurize and depressurize appropriate ones of the clutches and brake of the drive train in order to accomplish the several operational modes described above. The valve settings include Reel-In, Brake-On, Brake-Off and Free-Spool and are realized by movement of a control lever or the like. For safety reasons as well as for convenience of operation, centering springs urge the control valve towards the Brake-On position so that if the operator releases his control lever or the like, the winch is automatically immobilized.
The operator of these winch systems must pay careful attention to the position of his control lever or the like in order to control movement of a load in a safe and efficient manner. It is particularly important to avoid movement of the lever into the Disconnect position through misjudgment while a load is pulling on the cable to be released, creating unwanted slack, when dropping of the load stops or slows. Diversion of the operator's visual attention in order to guard against this occurrence is undesirable in many cses, particularly in such usages as on a log skidder where the operator must pay attention to controlling the vehicle itself in addition to operating the winch.
U.S. Patent application Ser. No. 574,807 of Edward E. Flesburg, filed May 5, 1975 for "WINCH AND FLUID CONTROL SYSTEM THEREFOR", commonly assigned herewith, now U.S. Pat. No. 4,004,779 issued Jan. 25, 1977, discloses means which enable the operator of such winch systems to determine when the control lever is approaching the Free-Spool position without necessarily relying on visual observation.